It's unusual to talk about 'wattage' in this context — it is more usually 'power', and very often, it is the 'current' that matters in a switching context.
However, I can see that here they may be in a low voltage / high current situation, which probably directed their choice of terminology.
I was unsure about the 'de' — but it is 'switching of high power loads', so I feel 'd' is probably more relevant here than (say) 'à'